The present invention relates to material testing devices and, more particularly, to a test device utilizing a solenoid for applying a test force to a material sample in a predetermined manner and for monitoring the effect of such force upon the sample.
Testing of many materials and machine components includes tests to determine the ability of the test samples to withstand either tensile or compressive forces, or both. Prior art devices capable of performing such tests have generally been complex in design and correspondingly expensive. One type of prior art testing device uses a test fixture including a pair of material-gripping jaws. One of the jaws is held stationary while the other jaw is moved by means of a servomotor rotating a threaded bolt which passes through the jaw mounting structure. A load cell is provided on the test fixture for monitoring the amount of force applied to the test material and providing an electrical output proportional thereto. Although this type of testing device permits a substantial range of force to be applied to the test material, control of the servomotor mechanism requires complicated control circuitry if the force applied to the test material and the rate of application of the force are to be controlled precisely.
Other testing devices utilizing hydraulic actuators for applying force to the test samples have also been used in the past. In one prior art system, a servovalve controls application of hydraulic fluid to the hydraulic actuator under control of a closed loop control circuit receiving an input from a load cell mounted on the test fixture. It will be appreciated that such a hydraulic system, while providing for substantial application of force to a test sample is large in size and presents significant problems with respect to the accuracy of force applied by the hydraulic actuator. The advantage of such a system over the servomotor type of testing device is that the hydraulic actuator may be connected directly to one of the material-gripping jaw mechanisms, thus eliminating the need for the threaded rod configuration required in the servomotor system and the attendant limitations on force level fluctuation resulting from inertia of the rod and servomotor.
Although the large prior art systems described above provide for material testing over large ranges of force levels, a need exists for a small, simple, and relatively inexpensive test device for applying a small test force to a material sample in which the material sample will experience minimal dimensional distortion. Such a device should be capable of providing extremely accurate force levels and force application rates and, further, should provide for storage of the maximum force level obtained, in the event of sample failure. It is also desirable to provide a pass/fail indication as well as a direct read out of the force level applied in order to minimize operator fatigue where a large number of samples are to be tested.